What's the Goal of Voter-ID Laws?

As states around the country enact or consider voter-ID laws, the battle formations are well-rehearsed. Conservatives who back the laws say that there’s a danger of fraudulent votes, which pollute the democratic process at best and swing elections at worst. Liberals who oppose them counter that there’s next to no evidence of actual voting fraud; that voter-ID laws wouldn’t stop that fraud anyway; and that the laws are actually intended to depress voter-turnout among the populations that are least likely to hold state-issued photo ID—students, the poor, minorities, and the elderly who are most likely to vote Democratic—and improve conservative prospects in elections, despite demographic changes that favor liberal candidates.